<select name="semestre">
  <option value=""></option>
  <option value="01" <? if($semestreSeleccionado == "1") echo "SELECTED"; ?>>01</option>
  <option value="02" <? if($semestreSeleccionado == "2") echo "SELECTED"; ?>>02</option>
  <option value="03" <? if($semestreSeleccionado == "3") echo "SELECTED"; ?>>03</option>
  <option value="04" <? if($semestreSeleccionado == "4") echo "SELECTED"; ?>>04</option>
  <option value="05" <? if($semestreSeleccionado == "5") echo "SELECTED"; ?>>05</option>
  <option value="06" <? if($semestreSeleccionado == "6") echo "SELECTED"; ?>>06</option>
  <option value="07" <? if($semestreSeleccionado == "7") echo "SELECTED"; ?>>07</option>
  <option value="08" <? if($semestreSeleccionado == "8") echo "SELECTED"; ?>>08</option>
  <option value="09" <? if($semestreSeleccionado == "9") echo "SELECTED"; ?>>09</option>
  <option value="98" <? if($semestreSeleccionado == "98") echo "SELECTED"; ?>>Pasante</option>
  <option value="99" <? if($semestreSeleccionado == "99") echo "SELECTED"; ?>>Titulado</option>
</select>